I have conceived, built, and successfully operated a machine that ties and then unties a necktie, using a four-in-hand necktie knot. The machine consists of 10 different electric motors that are coordinated by a computer so as to perform the above tasks on a tie hung from a platform located above the motors. The purpose of the machine is for entertainment although in principle, after the tie is tied, it could be removed from the platform and hung on a person""s neck as if it had been manually tied.
Each of the ten electric motors has an integral gearhead whose output shaft is attached to a potentiometer that provides feedback to an electronic power operational amplifier that drives the motor resulting in servomechanism operation that is well known to feedback control engineers. Each output shaft has an attached lever or pulley wheel or specially shaped structure to accomplish a given type of task (e.g. pulling or pushing or rolling or grabbing the tie) within the overall cycle. The motors are located on posts several feet high projecting up from a heavy baseplate approximately 1.5xc3x973 feet in size that in turn is mounted upon a wooden base. The input to each of the 10 servomechanisms, which controls how far it is to rotate, is an analog voltage coming from a D/A converter controlled by a personal computer. The computer runs a program that sequentially reads out a data set line by line. The data in each line consists of a first number which selects which motor is to be operated, a second number which determines how far it is to rotate, and a third number which determines how long the computer is to wait before reading out the next line, e.g. typically the duration of the motor motion. In the current version of the data set that successfully ties and unties the necktie, there are approximately 550 lines. It takes approximately 6 minutes to sequentially read out all of these lines, and therefore to tie and untie the necktie.
The most difficult challenge in automatically tying the four-in-hand knot is to push the wider part of the tie (henceforth labeled RTxe2x80x94for right tie) through the space between the first and second wraps of the RT around the narrow part of the tie (henceforth called LTxe2x80x94for left tie). In my design this guidance of the mechanically manipulated RT is facilitated by pulling the RT through a 3 inch diameter horizontally oriented support tube about which rotates an outer rotating tube over which RT has been previously wrapped (the second wrap). The first wrap of RT around LT has previously been manipulated to be outside and behind both concentric tubes so that when the RT is pulled through the support tube, it is automatically located between the first and second wraps. This use of a tube to guide RT as described above dominates the design and operation of the machine. It is explained more thoroughly in Section IV Method of Operation and in the various parts of FIG. 12. The rotary and support tubes can be raised and lowered a distance comparable to the length of the suspended RT. A horizontal tab is attached to the periphery of the rotating tube at its left end. When RT is engaged in the tab and the tube is rotated, RT can be wrapped around the tube by an amount controlled by the tube rotation. In summary, the support tube can be vertically moved to position the outer rotating tube at different heights and the RT ultimately gets pulled through the inner support tube. Hereinafter the term tube assembly is used to stand for the concentric rotary and support tubes.